Abstract: During the Cretaceous period, the lacewing superfamily Mantispoidea, with an assemblage of species possessing raptorial forelegs, have undergone a rapid species radiation, characterized by abundant species richness and high morphological plasticity. Nevertheless, the morphology and early evolution of the specialized predatory organ around the time of its origin in raptorial Mantispoidea have been poorly documented due to the rarity of fossil evidence, especially for the pre-Cretaceous fossils. Herein, a new genus and new species, i.e. Archarhachiberotha longitarsa J. Wang, Ren et Y. Wang gen. et sp. nov., was described from the Middle Jurassic Jiulongshan Formation of northeastern China. This new genus was characterized by the remarkable raptorial forelegs, i.e. typically elongated coxa, relatively less-swollen femur and rudimentary small femoral spines, and well-developed tarsi. Considering the peculiar morphological combination and antiquity of the new genus, it was assigned to be a stem-group lineage of Mantispoidea. Besides, the detailed analyses of morphology and biological functions of raptorial forelegs were made to conclude that the new genus evolved into an unknown but primitive raptorial type that was distinctly different from the extant morphological features and raptorial mechanisms. In addition, the evolutionary tendency of raptorial Mantispoidea herein summarized highlights morphological diversity and disparity between fossil and extant representatives, and provides a rare case to explore the entire evolutionary history of a specialized structure in one lineage. 

Key words: Evolutionary tendency, Functional morphology, Jiulongshan Formation, Mesozoic, New species, Predation